Apparatus for the production of encapsulated foaming concentrates

ABSTRACT

The present invention is directed to apparatus for compounding and pelletizing of chemical foaming agents in a high melt resin carrier and producing unique, uniform encapsulated and pelletized chemical foaming concentrates. More specifically, the present invention is directed to the compounding, encapsulating and pelletizing in a high melt resin carrier a highly loaded concentration (5 to 70 wt %) of foaming agents which include an endothermic foaming agent, an exothermic foaming agent or hybrid combinations of these two such that when incorporated into a thermoplastic resin to produce a foamed product will chemically react to form carbon dioxide, nitrogen or hydrogen or mixtures thereof as the active foaming gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/321,325,filed on Oct. 11, 1994, now abandoned, which is a divisional applicationof U.S. patent application Ser. No. 08/061,102 filed May 13, 1993entitled "PRODUCTION OF ENCAPSULATED CHEMICAL FOAMING CONCENTRATES","abandoned in favor of a continuous application, U.S. patent applicationSer. No. 08/404,142, filed Mar. 9, 1995, entitled `PRODUCTION OFENCAPSULATED CHEMICAL FOAMING CONCENTRATES,` Ser. No. 08/061,182 havingbeen" in turn is a divisional application of U.S. patent applicationSer. No. 07/974,109 filed Nov. 10, 1992 entitled "PRODUCTION OFENCAPSULATED CHEMICAL FOAMING CONCENTRATES", now U.S. Pat. 5,234,963,which in turn is a continuation-in-part application of U.S. patentapplication Ser. No. 07/882,279 filed May 13, 1992 entitled "PRODUCTIONOF ENCAPSULATED CHEMICAL FOAMING CONCENTRATES", now abandoned.

FIELD OF THE INVENTION

The present invention is directed to the process and apparatus for theproduction of encapsulated chemical foaming concentrates which includesthe compounding of chemical foaming agents in a resin carrier andpelletizing the concentrate under water at such conditions that thechemical foaming agent is encapsulated. These uniquely encapsulated andpelletized chemical foaming concentrates are used for foamingthermoplastics. More specifically, one embodiment of the presentinvention is the encapsulating of an endothermic foaming agent such ascitric acid and sodium bicarbonate in a resin carrier which whenincorporated into a thermoplastic polymer to be foamed will react toform carbon dioxide as the active foaming gas. Another embodiment of thepresent invention is the encapsulating of an exothermic foaming agentsuch as an azo compound or a hydride in a resin carrier which whenincorporated into a thermoplastic polymer to be foamed will react toform nitrogen or hydrogen respectively as the active foaming gas. Stillanother embodiment of the present invention is the encapsulating of anendothermic foaming agent with an exothermic foaming agent at levelsfrom 10/90 to 90/10 wt % to obtain a hybrid foaming agent concentrateexhibiting the best properties of each foaming agent system.

BACKGROUND OF THE INVENTION

Foaming of thermoplastics in the majority of applications is nowaccomplished with exothermic foaming agents, usually azo compounds,which when admixed with the desired thermoplastic polymer in an extruderor molding machine are heated above their decomposition temperatures,and produces nitrogen which forms the cell structure in the molded orextruded part. However, in the compounding and producing of concentratesof these exothermic foaming materials the chemical reaction of thefoaming agents is not suppressed in any of the current processesemployed. Approaches vary, one is compounding the exothermic foamingagents in a very low melting material so that when mixing the foamingagent with the material the decomposition temperature is not reached;however, the low melting material may not be fully compatible with thedesired thermoplastic polymer used to produce a foamed part or product.Another approach is to attempt to produce the concentrate at maximumflow rates or minimum residence times in the extruder. However, theconditions heretofore used are often contrary to controlling thedecomposition of the foaming agent and the foaming agent reacts,releasing the gas and the pellets containing the foaming agent arealready foamed or have lost the gas. These pellets are larger than thedesired pellet size and have an outer surface which shows the loss ofgas. Therefore, when such pellets are added to the thermoplastic resindesired to be foamed there is a non-uniform amount of unreacted chemicalfoaming compounds in these pellets to foam the thermoplastic and thefoamed product is neither consistent nor uniform causing substantialoff-specification and rejected product.

Attempts to produce endothermic chemical foaming concentrates in thehigh melting thermoplastic resins has not been attempted since thetemperatures in an extruder to compound exceed the reaction temperatureof such foaming agents. Attempts may have been made to foamthermoplastic polymers with endothermic chemical foaming agents bymixing them in waxy carriers; however, the ability to mix the foamingagent uniformly with a high melting polymer in a single pass through anextruder and produce a consistent foamed product was impossible due tomelting temperature parameters between the waxy material, the foamingagents and the high melting thermoplastic resins such as polypropylene,polystyrene or polyethylene to be foamed.

U.S. Pat. Nos. 5,037,580; 5,045,570; 5,009,809 and 5,009,810 disclosechemical foaming agents specifically a polycarboxylic acid and aninorganic carbonate which are surface treated before compounding withmaterials such as mono-glycerides, stearic acid, silane coupling agents,fatty acids, titanates and mixtures thereof. In each patent, theadmonition is given regarding compounding that: "The extruder must,however, be operated below about 149° C. in order to keep theendothermic blowing agent from foaming prematurely." Hence, it is clearfrom the patents themselves that these foaming agents were not to becompounded in high melting resins that had melting or compoundingtemperatures above 149° C. The patents also disclose as the material tosurface treat the blowing agent a component selected from the groupmonoglycerides, stearic acid, silane coupling agents and mixturesthereof. U.S. Pat. No. 5,045,570 additionally includes thedi-glycerides, fatty acids, fatty acid salts, hydrotitinates andzirconates as materials to surface treat the blowing agents.

SUMMARY OF THE INVENTION

The present invention is directed to the process and apparatus forcompounding and pelletizing of chemical foaming agents in a hightemperature melting resin carrier (resins melting above 149° C.) andproducing unique, uniform encapsulated and pelletized chemical foamingconcentrates. More specifically, the present invention is directed tothe compounding, encapsulating and pelletizing in a high temperaturemelting resin carrier, at highly loaded concentrations (5 to 70 wt %),of a foaming agent selected from an endothermic foaming agent, anexothermic foaming agent or a hybrid combination of endothermic andexothermic foaming agents such that when incorporated into athermoplastic resin to produce a foamed product will chemically react toform a carbon dioxide, nitrogen, hydrogen or mixtures thereof as theactive foaming gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational schematic of the preferred equipment which isused to carry out the compounding, encapsulation and pelletizing of ahigh melting resin carrier and chemical foaming agents to producefoaming agent concentrates (5 to 70 wt % active levels) according to thepresent invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a foaming agent concentrate of anendothermic chemical foaming agent, an exothermic chemical foaming agentor a hybrid mixture of endothermic and exothermic foaming agents iscompounded and encapsulated in a resin carrier, without foamingoccurring so that the encapsulated and pelletized concentrate may beblended uniformly with the desired thermoplastic resin and passedthrough an extruder or injection molding machine for production of aconsistent foamed product. The uniqueness of the process of the presentinvention allows the carrier to be a high melting thermoplastic resinand thus be the same resin which is to be foamed; for example if highdensity polyethylene is foamed the carrier chosen is high densitypolyethylene. However, the resin carrier need not be the identical resinbut a resin having a lower melting point or lower density but iscompatible with the thermoplastic being foamed. What is common to thefoaming concentrates of the present invention is the process by whichthey are produced.

The process for the production of a foaming agent concentrate accordingto the present invention comprises compounding or mixing a resin carrierwith the chemical foaming agent under processing or mixing zones ofhigher operating pressures, forcing the mixture of foaming agent andresin carrier through a die forming strands of mixture, and pelletizingunder water the strands using pressurized and cooled water to quicklycool and solidify the outer surface of the resin carrier and toencapsulate the foaming agents in the carrier, the encapsulationoccurring under water at water pressures between 10 and 200 pounds persquare inch gauge (psig) and water temperatures between 40° and 180° F.It has been found that when the carrier and foaming agent mixture israpidly cooled and a positive pressure is maintained in the watercutting or pelletizing chamber, the chemical foaming agent isencapsulated without substantial reaction within the resin carrier as apelletized concentrate. By substantial reaction is meant, that thepellets produced by the process of the present invention differ from thepellets of foaming agents now produced in that the gases formed, if any,are entrapped in the resin carrier. In contrast, pellets of foamingagents now produced use lower melting materials, often waxes, to reducereaction and gas release or alternately the pellets are foamed or evencollapsed showing evidence of reaction of the foaming agent during thecompounding of the foaming agents (these pellets increasing in sizebefore collapse). With pellet concentrates (containing 5 to 70 wt %unreacted foaming agents) of the present invention, the chemicalreaction of the chemical foaming agent is contained, prevented orsuppressed due to the sudden freezing or solidification of the resincarrier which keeps the gas, either carbon dioxide, nitrogen or hydrogenor mixtures thereof, if any is formed, from escaping from theencapsulated chemical foaming concentrate pellets thus containing,preventing or suppressing the chemical react ion. In the presentinvention the concentrate pellets contain in each pellet all the foamingagent necessary for the chemical reaction to occur to produce the activefoaming gas so that the addition of these concentrate pellets withthermoplastic resins in an injection molding machine, for example,produce a uniform product with higher concentrations of foaming gas thanheretofore obtained. For example, if an acid and base are foamingagents, both acid and base are in the same concentrate pellet atconcentrations that will provide more foaming gas than obtained byprevious methods.

Referring now to FIG. 1, the apparatus 10 used to carry out the processof the present invention is shown. The compounding, encapsulating andpelletizing apparatus 10 includes a compounding or mixing extruder 12.An extruder having more than one mixing zone is preferred; however, theextruder is required to have the operating pressures in each operatingor mixing zone essentially the same or slightly higher. The operatingpressures in the zones are maintained such that the chemical reaction ofthe foaming agent is contained, prevented or suppressed and nosubstantial decrease in operating pressure is permitted which allows thegaseous reaction product of the foaming agents to be produced eventhough the temperatures exceed reaction or decomposition temperatures ofthe foaming agents. When water is present either as part of thethermoplastic carrier resin or the foaming agents, the water must beremoved before the foaming agents and carrier resin are compounded orthoroughly mixed and reach the reaction temperature of the foamingagents. In the initial stage of the extruder 12, as the temperature ofthe resin is brought to its melting temperature, the mixture is raisedto a temperature above 212° F., the boiling point of water, and in thatzone the water is vented through a vent 13, which may either be openedto the atmosphere or connected to vacuum. Even before the foaming agentsare added to the extruder 12, any water is removed from the foamingagents by a separate piece of equipment such as a drier. Extruder 12 maybe a single screw extruder but a double screw mixing extruder having aplurality of vents 13 is preferred. The extruder may have a side feeder14. The extruder 12 is mounted on a pedestal or base 15 which may be onrollers (not shown). In most instances the chemical foaming agentstogether with a resin carrier are introduced into the hopper 16 of theextruder 12, while venting water through a vent 13. In other instances,the chemical foaming agents or the resin carrier are added through theside feeder 14. As will be explained in more detail hereinafter, theresin carrier of the present invention is preferably a high temperaturemelting resin and usually a thermoplastic resin which is essentially thesame as the desired thermoplastic to be foamed. According to the presentinvention, if polyethylene is to be foamed, the carrier resin used toform the concentrate is preferably polyethylene; if polycarbonate is tobe foamed, then the carrier resin is preferably polycarbonate orpolystyrene is to be foamed, then the carrier resin is preferablypolystyrene. This preference is not meant to infer that a foaming agentconcentrate of the present invention using one carrier resin cannot beused to foam another thermoplastic resin. The melt index of the carrierresin may be higher than that of the resin being foamed. The hopper 16is kept one-third to two-third full so that the neck 18 of the hopper 16is full for a single screw extruder. With a twin screw extruder, thiscondition is not necessary. The chemical foaming agents are compoundedwith the resin carrier in the extruder as the mixture move from the sidefeeder 14 or hopper 16 to a die 20. It is noted that the extruder 12 hasno screen pack or other structure such as vents or entry points whichwill permit any pressure drops once the reaction temperature of thefoaming agents is reached or more specifically, no structure whichpermits the foaming gases to form and escape from the extruder 12, thuspreventing the reaction of the chemical foaming agents to begin duringthe compounding even though the temperature is at or above thetemperature for the reaction to occur. The die 20 has a short land,meaning the distance the materials flow through the die from inside theextruder to the outside of the die. The land lengths are less than 0.25inches which is half to one-quarter the land length of a normal die. Thenumber of opening and size of the opening in the die 20 may varydepending on the materials being concentrated but generally a die havinga single circle of die openings of about 0.085 to 0.125 inches indiameter will be suitable for most thermoplastic resins.

A water chamber or water cutting and pelletizing chamber 24 surroundsthe outer surface of die 20 and is connected directly to the end of theextruder 12. In chamber 24 is an under water pelletizer which cuts thestrands of foaming agent concentrate which is forced through the dieopening in die 20. Rotating in chamber 24 are a plurality of cutters 26which are on the end of rod 28 and are essentially in contact with theouter face of die 20. The cutters 26 are within 1/64 inch from the faceof die 20, and the number of cutters 26 and speed of rotation are suchthat the pellets formed are the standard size of 1/8 inch in length. Therod 28 may be rotated at a desired speed by motor 30 and adjusted by agear box 32. The strands of compounded chemical foaming agents which areforced out the die openings are immediately cut off into pellets, thecutting or pelletizing being done under the water which fills thechamber 24. It has been observed that no foaming occurs as the strandsfirst come from the die and are cut even with a pressure let down. 0fsignificance to the present invention, the chamber 24 is maintainedunder a positive pressure and the water is cooled so that the outersurface of the pellets formed are quickly solidified or morespecifically, the viscosity of the resin is increased to encapsulate thechemical foaming agent pellet concentrates. The pellets are encapsulatedbefore the gaseous reaction product is produced and released, thereaction cannot occur and is contained, prevented or suppressed while inthe extruder and is encapsulated before the reaction occurs in the waterchamber 24. Even though there is a pressure drop from the end of the die20 into the chamber 24, the conditions in the chamber 24 including thetime before the strand is cut to form a pellet are such thatencapsulation occurs and the chemical reaction between the foamingagents is contained, prevented or suppressed. These conditions are indirect contrast to conditions now used in attempting to produce foamingagent concentrates where the carrier used is as low melting as possibleso that the mixture is extruded at the lowest possible temperature andwhere the concentrate mixture is extruded into a chamber that does nothave sufficient positive pressures to contain, prevent or suppress thechemical reaction of the foaming agent.

The pressure and temperature of the water in chamber 24 is controlled inmost part by the pressure and temperature of the water entering by line34 into chamber 24. The encapsulated and pelletized pellets of thechemical foaming agents are removed from the chamber 24 by line 36. Theheight or head of line 36 will also be a part of thepressure/temperature control. Specifically, a gate valve 37 controlsback or head pressure in line 36. Line 36 empties into a separation duct38 which has a number of screens (not shown) which separate the pelletsfrom the water. The pellets are directed to a drier 50 and the water isdirected to a reservoir 40. The water in the reservoir 40 may be heatedby heater 41, if necessary or during start-up, and is recycled tochamber 24 by pump 42. Pump 42 is larger than conventional pumps used inunder water pelletizers and provides the desired positive pressure inthe water chamber 24. The size of pump 42 will need to correspond to anydesired pressure in the system. Before returning to the chamber 24, thewater is cooled in chiller 44. The desired pressure in chamber 24 iscontrolled not only by the pressure of pump 42 but by the height or headof line 36 or gate valve 37 prior to discharge of line 36 into drier 50.The pressure in the water system is measured by gauges 46 or 48. Gauge48 is usually the gauge used to measure the pressure in chamber 24 andcontrol the water system. The temperature in chamber 24 is controlled bythe amount of cooling done in chiller 44. The availability of cold waterand the season will determine the amount of cooling necessary before thewater leaving chiller 44 enters line 34 for return to chamber 24. Thedrier 50 comprises a series of air jets (not shown) in the bottom wall52. Central to the drier 50 is a lift auger 54 which is rotated by motor56. The lifting of the pellets in the presence of the dry air streamremoves the water and the dried pellets are removed from the drier 50 byoutlet pipe 58. Air and entrained water is removed by outlet 60 at thetop of drier 50. The dried pellets are collected on a classifier or in alined box 70. A classifier 70 is preferred in that the vibration willremove any water that comes over with the pellets from the drier 50.

The chemical foaming agent concentrates of the present invention, byemploying the above described equipment and process conditions, exhibitthe same color and appearance of the carrier resin. The concentratepellets of the present invention are clear and have a generally uniformsize. In contrast, all competitive materials now in the market place aregenerally white in color due to foaming of the additive ingredients, arenon-uniform in size, are larger than the desired and extruded pelletsize and may include collapsed pellets.

While the apparatus 10 described is a preferred embodiment used toproduce the encapsulated and pelletized chemical foaming agents of thepresent invention, the specifics of the apparatus and process willdepend on the specific foaming agents used, water present and thespecific carrier resin employed. For example, different temperatures areemployed in the extruder to compound and mix specific chemical foamingagents with specific resin carrier (used to emphasis the resin whichencapsulates the foaming agents to produce the concentrates of thepresent invention) due to the carrier's melting temperature as well asthe temperature required for homogeneous mixing of the foaming agent andforcing the mixture through the extruder die 20, and likewise, thetemperature of the water and the pressure within the water pelletizingchamber 24 will vary depending on the specific resin carrier employed.While not specifically shown in the schematic, a drier is used to drythe foaming agents so that no more than 1 to 2 wt % water is introducedto the extruder 12.

The foaming agents encapsulated or concentrated by the apparatus andprocess of the present invention are primarily for thermoplasticpolymers or resins but may include certain rubbery materials.Thermoplastic resins which are now currently foamed include low densitypolyethylene (LDPE), high density polyethylene (HDPE), polypropylene(PP), polystyrene (PS), polycarbonates (PC), polyesters, nylon, and ABS,acetal, acrylic, ethylene vinylacetate copolymers (EVA), fluoroplastic,modified phenylene oxide based, polyurethane-thermoplastic, polysulfonepolymers. These thermoplastic resins may be used as the resin carrier inproducing the encapsulated foaming concentrates of the presentinvention. In addition, thermoplastic resins such as ethylene acrylicacid copolymer (EAA), ethylene methacrylic acid copolymers (EMA),polyvinylchlorides (PVC) and the ethylene-based copolymers neutralizedwith metal salts, forming ionic clusters and known as ionomers, whichare not now commonly used to produce foamed products may be included asresin carriers for the foaming agents of the present invention. Theinclusion of resins not used heretofore as well as the modifiedengineering resins which are presently becoming available illustratesthat the process of the present invention extends the current technologyfor foaming thermoplastic polymers and resins.

The resin carrier employed usually is the same thermoplastic resin asthe resin which is desired to be foamed. In other words, if high densitypolyethylene is the thermoplastic which will be foamed to produce afoamed polyethylene product with the encapsulated chemical foamingagents of the present invention, then polyethylene is used as thecarrier resin. Since the carrier resin becomes part of the foamedproduct, the polyethylene used as the carrier resin may be the same asthe polyethylene to be foamed. In some instances the resin carrier willnot be the identical thermoplastic resin as the resin to be foamed. Tomake certain that the choice of resin carrier is understood, if thethermoplastic resin to be foamed is polycarbonate, then the resincarrier may be a polycarbonate. The choice of carrier heretofore was notcompletely based on the thermoplastic resin to be foamed but was acompromise between a low melting material that was compoundable with aspecific foaming agent and was somewhat compatible with the desiredthermoplastic resin. Even the choice of foaming agent was a compromisebased on the reaction temperature of the foaming agent and thetemperature required to melt and extrude the desired thermoplastic resinto be foamed. These compromises have been overcome by the process of thepresent invention. The choice of foaming agent and the resin carrier isnow based on improving the performance of foaming the desiredthermoplastic resin.

One significant feature of the present invention is that the apparatusand process of the present invention will encapsulate in a hightemperature melting resin carrier an organic acid and a base which areendothermic chemical foaming agents. The encapsulation of endothermicfoaming agents of the process of the present invention preferablyinclude the encapsulation of a carbonate as the base and sufficientorganic acid such that when incorporated in the desired thermoplasticresin the two agents react chemically to form carbon dioxide. Naturalcarbonates such as calcium carbonate or sodium bicarbonate are effectivecarbonates as one of the endothermic foaming agents of the presentinvention. Preferred carbonates are lithium carbonate and sodiumbicarbonate. Synthetic carbonates also may be used. Synthetic carbonatessuch as the hydrotalcite-like compound, DHT4A made by Kyowa ChemicalIndustry Co., Ltd. , is a suitable carbonate for the foaming agents ofthe present invention. Other suitable synthetic carbonates are thedihydroxyaluminum sodium carbonates, dihydroxyaluminum calciumcarbonates or the Halogard products made by Chattem Chemicals ofChattanooga, Tenn. While other carbonates may be used, either natural orsynthetic, the carbonates specifically referred to herein are all FDAapproved to be used in food grade resins or products handling food.

The organic acid used as the other part of the endothermic foaming agentof the present invention is preferably either malic or citric acid. Bothacids are solids at room temperature and will react completely with acarbonate to form carbon dioxide and water. Any other organic acid whichwill react with the carbonate to form carbon dioxide and water may beused, even the lower molecular weight acids which are normally solids.Acids such as maleic acid, formic acid, glutaric acid, oxalic, succinicacid, fumaric and pyruvic acid which are normally solids at roomtemperature may be employed.

The carrier and endothermic foaming agents, preferably surface treatedas will be described in more detail hereinafter, are premixed. Thecarrier thermoplastic resin, usually in the form of pellets or powder,is mixed with the endothermic chemical foaming agents, such as citricacid and sodium bicarbonate, in a ribbon or Henschel mixer. The amountof acid and carbonate are in stoichiometric amounts or the weightproportions in which the two specific materials react, and the combinedamount of the two endothermic foaming agents is at least 5 to 70 wt % ofthe combined mixture. This mixture is introduced into the extruder 12 ofthe apparatus 10 of the present invention and compounded. The mixture isforced through a die 20 where the strands are cut under water maintainedat a positive pressure greater than 15 psig and cooled. The outersurface of the carrier quickly solidifies and encapsulates the acid andbase in the carrier resin.

The apparatus and process of the present invention also will encapsulatein a high temperature melting resin carrier exothermic chemical foamingagents. Exothermic chemical foaming agents include the azo compoundssuch as azodicarbonamide and modifications or derivatives thereof(CELOGEN AZ, CELOGEN AZ 3990, CELOGEN AZ NP products of UniroyalChemical, a div. of Uniroyal, Inc. ) which on decomposition yieldnitrogen, carbon monoxide and carbon dioxide; other compounds whichyield nitrogen such as p,p-oxybis benzene sulfonyl hydrazide, otherhydrazides or p-toluene sulfonyl semicarbazide, dihyroxydiazinone,5-phenyltriazole; and compounds which yield hydrogen such as sodiumborohydride or other hydrides all of which are encapsulated by theapparatus and process of the present invention.

Still further, the apparatus and process of the present invention willencapsulate in a high temperature melting resin carrier a hybrid ofendothermic and exothermic chemical foaming agents. A hybridencapsulated chemical foaming concentrate is produced by mixing both anendothermic foaming agent, for example, malic acid and lithiumcarbonate, with an exothermic foaming agent, for example, sodiumborohydide. The concentration of each foaming agent ranges such that theratio of endothermic to exothermic is between 10/90 and 90/10 wt %.

The encapsulated foaming agents of the present invention are illustratedby the following examples.

EXAMPLE 1

An endothermic encapsulated foaming agent concentrate is produced withhigh density polyethylene at a chemical foaming agent concentration of25 wt %. The blend of organic acid to base is at a ratio of 0.7/1.0(41.2 wt % acid/58.8 wt % base). A specific formula consists of thefollowing:

a) 75 wt % TR885 HDPE (a high density polyethylene product of PhillipsChemical Company);

b) 10.3 wt % citric acid;

c) 14.7 wt % sodium bicarbonate.

Components b) and c) are each separately pretreated with 1 to 10 wt %glycerol monostearate or pentaerithritol teta-stearate in a Henschelmixer.

The component a) and pretreated components b) and c) are premixed in aHenschel mixer or a ribbon blender and introduced to an extruder asdescribed in FIG. 1. The extruder is a twin screw Werner & Pfleidererextruder, the die has a single circle of 12 openings having a 0.100 inchdiameter. The conditions in the water chamber are maintained at 10 to 60psig and at a temperature of between 40° and 130° F.

The pelletized concentrate produced is a uniform pellet in size andshape, with no collapsed pellets or pellets which are foamed.

EXAMPLE 2

An endothermic encapsulated foaming agent concentrate is producedsimilarly as in Example 1 except malic acid and lithium carbonate areused. It has been found that this combination of foaming agentconcentrate produces a very small and uniform cell structure whenincorporated into polyethylene to produce the foamed polyethylene.

EXAMPLE 3

An endothermic encapsulated foaming agent concentrate is produced withpolycarbonate at a chemical foaming agent concentration of 25 wt %. Aspecific formula consists of the following:

a) 75 wt % CD200 PC (a polycarbonate product of Mobay Chemical Company);

b) 18.75 wt % malic acid (a product of Barteck Chemical Company);

c) 6.25 wt % lithium carbonate (a product of Cyprus Chemicals).

Components b) and c) are each separately pretreated with 1 to 10 wt %glycerol monostearate or pentaerithritol teta-stearate in a Henschelmixer.

The component a) and the pretreated components b) and c) are premixed ina Henschel mixer or a ribbon blender and introduced to an extruder asdescribed in Example 1. The conditions in the extruder are at highertemperatures because the functional carrier is polycarbonate; however,the conditions in the water chamber are approximately the same as inExample 1.

EXAMPLE 4

An exothermic encapsulated foaming agent concentrate is produced withhigh density polyethylene at a chemical foaming agent concentration of25 wt %. A specific formula consists of the following:

a) 75 wt % TR885 HDPE (a high density polyethylene product of PhillipsChemical Company);

b) 25 wt % CELOGEN AZ (an azodicarbonamide product of Uniroyal Chemical).

The components a) and b) are premixed in a Henschel mixer or a ribbonblender and introduced to an extruder as described in Example 1. Theconditions in the water chamber are maintained at 15 to 100 psig and ata temperature of between 40° and 130° F.

The pellets produced are uniform in size and shape, with no collapsedpellets or pellets which are foamed.

EXAMPLE 5

An exothermic encapsulated foaming agent concentrate is producedsimilarly as in Example 4 except CELOGEN TSH or CELOGEN OT (a p-toluenesulfonyl hydrazide or p,p-oxybis benzene sulfonyl hydrazide product ofUniroyal Chemical) or sodium borohydride are used.

EXAMPLE 6

A hybrid endothermic and exothermic encapsulated foaming agentconcentrate is produced with high density polyethylene at a chemicalfoaming agent concentration of 25 wt %. A specific formula consists ofthe following:

a) 75 wt % TR885 HDPE (a high density polyethylene product of PhillipsChemical Company);

b) 20 wt % CELOGEN AZ (an azodicarbonamide product of Uniroyal Chemical);

c) 2.06 wt % citric acid; and

d) 2.94 wt % sodium bicarbonate. Components c) and d) are eachseparately pretreated with 1 to 10 wt % glycerol monostearate orpentaerithritol teta-stearate in a Henschel mixer.

The components a), b) and pretreated components c) and d) are premixedin a Henschel mixer or a ribbon blender and introduced to an extruder asdescribed in Example 1. The conditions in the water chamber aremaintained at 15 to 100 psig and at a temperature of between 40° and130° F.

The pellets produced are uniform in size and shape, with no collapsedpellets or pellets which are foamed in the concentrate produced.

A material having very different characteristics than known treatingmaterials, such as glycerol monostearate or pentaerithritolteta-stearate used in the previous Examples, has been found to surfacetreat the foaming agents or more specifically each component of thefoaming agent composition which has any propensity to be hydrophilic.This material is glycerol tristearate (GTS) a product of PATCO, adivision of American Ingredients. Each component of the foaming agent istreated separately by adding the component, such as the sodiumbicarbonate or citric acid powder, to a high intensity mixer. Such amixer is a Henschel mixer and enough foaming agent component is added tocover the blades. The mixer is started at low speeds and added to thecomponent is 2 wt % of glycerol tristearate (GTS), based on the weightof component added to the mixer. Although 2 wt % of the GTS ispreferred, levels of 0.5 wt % to 10 wt % may be used to surface treatthe foaming agent components and all materials which may be added to thecomposition which may be hydrophilic. A hydrophobic foaming agents, suchas the azo materials, do not require surface treating. The mixer blendsthe mixture on high speeds for approximately 2 minutes. A maximum of 4minutes of mixing is sufficient to treat the component. The surfacetreatment is conducted at room temperature and no high temperatures orlong periods of mixing are required unlike the procedure required forknown materials, such as when using the glycerol monostearate. To testthe characteristics of a foaming agent component treated with GTS, thesurface treated powder is dropped into water and the powder floats onthe surface. Without the surface treating of the foaming agent with theGTS, the powder when dropped into water will settle to the bottom of thevessel holding the water. This surface treating step will enhance thequality of the foaming agent concentrates of the present invention inthat the ultimate objective is to eliminate all water prior to thecompounding of the concentrate.

The elimination of water prior to the compounding step must beemphasized to obtain an optimum concentrate product. To eliminate water,the foaming agents are first dried. Then the dr led foaming agents aresurface treated. The surface treating of the foaming agent components isone way to eliminate water by making sure that water is not absorbed bythe foaming agents and brought into the system with any of thecomponents making up the concentrate. Most of the carbonate componentsand acid components are materials which will absorb water. Another stepwhich has been found successful to the elimination of water is to ventthe extruder at a point before reaching the reaction temperature of thefoaming agents to form the reaction gas. Thus, the venting in the stageimmediately after the components of the foaming agent concentrate areadded to the extruder will take off water (heating the mixture ormaterials above 212° F.) but before the reaction temperatures of thefoaming agents is reached.

Additional examples are set forth, which emphasize the elimination ofwater which illustrate conditions of operation for long run periodswhich are not always obtainable when even small amounts of water enterthe extruder during the concentration process.

EXAMPLE 7

To 49 pounds of dihydroxyaluminum sodium carbonate (DASC, a product ofChattem Chemical) in a Henschel mixer operating at low speed is added 1pound (2 wt %) of glycerol tristearate (a product of PATCO). The mixeris turned to high speed for approximately 2 minutes to blend themixture. A sample of the mixture is dropped into water and the DASCpowder floats on the surface.

This simple procedure is used to treat or surface coat all components ofthe foaming agent concentrate that has any propensity to be hydrophilic.Other carbonates, such as sodium bicarbonate or aluminum hydroxidemagnesium carbonate or the acids such as citric acid or malic acid aretreated by this same simple procedure.

EXAMPLE 8

An endothermic encapsulated foaming agent concentrate is produced withan ethylene vinylacetate copolymer carrier resin at a chemical foamingagent concentration of 25 wt %. A specific formulation consists of thefollowing:

a) 74.5 wt % ethylene vinylacetate copolymer;

b) 10.3 wt % citric acid;

c) 14.7 wt % of a mixture of sodium bicarbonate, dihydroxyaluminumsodium carbonate (DASC) and aluminum hydroxide magnesium carbonate(HALOGARD AM, a product of Chattem Chemical);

d) 0.5 wt % calcium oxide.

Component b) and each of the components of c) are treated as set forthin Example 7 above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 30 to 60psig and at a temperature of between 80° and 130° F. It is noted thatventing is used. In addition to these conditions, calcium oxide wasadded to entrap any water in the foaming agent components.

The pelletized concentrate produced is a uniform pellet in size andshape, showing no foaming of the pellet.

EXAMPLE 9

An endothermic encapsulated foaming agent concentrate is produced withpolystyrene as the carrier resin at a chemical foaming agentconcentration of 25 wt %. A specific formulation consists of thefollowing:

a) 74.5 wt % polystyrene;

b) 10.7 wt % citric acid;

c) 15.3 wt % of a dihydroxy aluminum sodium carbonate (DASC);

d) 0.5 wt % calcium oxide.

Component b) and component c) are treated as set forth in Example 7above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 30 to 60psig and at a temperature of between 80° and 120° F. It is noted thatventing is used. In addition to these conditions, calcium oxide wasadded to entrap any water in the foaming agent components.

The pelletized concentrate produced is a uniform pellet in size andshape, showing no foaming of the pellet.

EXAMPLE 10

An endothermic encapsulated foaming agent concentrate is produced withan ionomer resin (Allied Signal Ionomer 272) as the carrier resin at achemical foaming agent concentration of approximately 55 wt %. Aspecific formulation consists of the following:

a) 43.7 wt % Ionomer resin (Allied Ionomer 272);

b) 23 wt % citric acid;

c) 32.8 wt % of a mixture of sodium bicarbonate and dihydroxy aluminumsodium carbonate (DASC);

d) 0.5 wt % calcium oxide.

Component b) and each component of component c) are treated as set forthin Example 7 above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 30 to 60psig and at a temperature of between 60° and 110° F. It is noted thatventing is used. In addition to these conditions, calcium oxide wasadded to entrap any water in the foaming agent components.

The pelletized concentrate produced is a uniform pellet in size andshape, showing no foaming of the pellet.

EXAMPLE 11

An endothermic encapsulated foaming agent concentrate is produced withan polypropylene resin as the carrier resin at a chemical foaming agentconcentration of approximately 25 wt %. A specific formulation consistsof the following:

a) 74.5 wt % of a mixture of polyethylene and polypropylene (thepolypropylene a product of Exxon Chemical);

b) 10.3 wt % citric acid;

c) 14.7 wt % of dihydroxy aluminum sodium carbonate (DASC);

d) 0.5 wt % calcium oxide.

Component b) and each component of component c) are treated as set forthin Example 7 above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 30 to 60psig and at a temperature of between 100° and 130° F. It is noted thatventing is used. In addition to these conditions, calcium oxide wasadded to entrap any water in the foaming agent components.

The pelletized concentrate produced is a uniform pellet in size andshape, showing no foaming of the pellet.

EXAMPLE 12

An endothermic encapsulated foaming agent concentrate is produced withan polystyrene resin as the carrier resin at a chemical foaming agentconcentration of approximately 10 wt %. A specific formulation consistsof the following:

a) 89.75 wt % of polystyrene (a product of Huntsman Chemical);

b) 8.00 wt % sodium borohydride (a product of Morton International);

c) 2.00 wt % stearic acid (a product of Witco Chemical);

d) 0.25 wt % calcium oxide.

Component b) is treated with between 3 and 10 wt % GTS and component c)is treated as set forth in Example 7 above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 10 to 60psig and at a temperature of between 40° and 130° F. In addition tothese conditions, calcium oxide was added to entrap any water in thefoaming agent components. The pelletized concentrate produced is auniform pellet in size and shape with no collapsed pellets. Thisconcentrate is a complete additive package with the base, sodiumborohydride, and the acid, stearic acid, combined into a single pellet;contrary to the salt and pepper blends available commercially.

EXAMPLE 13

An endothermic encapsulated foaming agent concentrate is produced withan ionomer resin as the carrier resin at a chemical foaming agentconcentration of approximately 20 wt %. A specific formulation consistsof the following:

a) 79.75 wt % of Allied 272 Ionomer (a product of Allied Signal);

b) 16.00 wt % sodium borohydride (a product of Morton International);

c) 4.00 wt % stearic acid (a product of Witco Chemical);

d) 0.25 wt % calcium oxide.

Component b) is treated with between 3 and 10 wt % GTS and component c)is treated as set forth in Example 7 above.

The component a) and the pretreated components b) and c) together withthe calcium oxide are premixed in a Henschel mixer and then introducedinto an extruder as described in FIG. 1. The extruder is a twin screwWerner & Pfleiderer extruder and was vented in the first zone at 18-20in. Hg. The conditions in the water chamber are maintained at 10 to 60psig and at a temperature of between 40° and 130° F. In addition tothese conditions, calcium oxide was added to entrap any water in thefoaming agent components. The pelletized concentrate produced is auniform pellet in size and shape with no collapsed pellets. Thisconcentrate is a complete additive package with the base, sodiumborohydride, and the acid, stearic acid, combined into a single pellet;contrary to the salt and pepper blends available commercially.

These examples are merely illustrative of the present invention and manymodifications and variations are possible.

We claim:
 1. An apparatus for the production of an encapsulated chemicalfoaming concentrate in a thermoplastic resin which comprises:athermoplastic extruder said extruder including a mixing zone with meansfor venting water from said mixing zone, said extruder further includinga compounding zone in which said extruder compounds a mixture of athermoplastic resin carrier and foaming agents, said compounding zonehaving means to maintain positive pressure within the compounding zoneof said extruder such that there is no substantial reduction inpressure, said extruder having an outlet end; a die at the outlet end ofsaid extruder, said die having a plurality of openings, a short landlength, less than 0.25 inches, and an outer face; a plurality of cutterblades at said outer face of said die which cut said mixture intopellets as it is extruded from the openings of said die; a water chambersurrounding said outer face of said die in which said pellets aresubjected to cooled water (at a temperature from 400° to 130° F.) underpositive pressure; and means for circulating water to said water chamberand maintaining a positive pressure greater than 15 psig in said waterchamber.
 2. An apparatus according to claim 1 which further includesmeans to cool the water in said chamber.
 3. An apparatus according toclaim 1 which further includes:an inlet line and an outlet line to saidwater chamber and a gate valve in said outlet line to provide backpressure in said out let line to control the positive pressure in saidwater chamber.
 4. An apparatus according to claim 3 wherein said meansfor circulating water and said valve in said outlet line maintain saidpositive pressure in said water chamber between 15 and 100 psig.
 5. Anapparatus according to claim 1 which further includes:means torecirculate and cool said water to said water chamber.